There have been many developments in the art of equipment for drilling holes in earth formations, including relatively soft as well as medium and hard formations. For example, in relatively soft formations so-called rotary drilling equipment is typically used in drilling wells and blastholes. However, as the hardness of the formation increases, rotary drilling becomes inefficient and expensive due to frequent requirements to repair the drilling equipment including replacement of the drillbit. In relatively hard formations downhole reciprocating piston pressure fluid operated percussion type tools are more effective in hole formation. Downhole percussion tools typically utilize a so-called button type bit, that is a bit with a relatively flat or angled transverse face with plural hard metal inserts disposed thereon for impacting and breaking the formation as the bit transfers the energy of reciprocating piston hammer blows to the formation and while indexing or rotation of the bit is undertaken. Chip evacuation is carried out by spent working fluid, normally compressed air.
Formations of intermediate hardness are sometimes the most difficult to penetrate efficiently since they do not respond well to drilling with strictly rotary type equipment and rotary bits or with strictly percussion type equipment and bits. A so-called claw bit has been developed for drilling, primarily in relatively soft formations, and utilizing conventional rotary drilling equipment. Heretofore this type of bit has not been adapted for use with percussion type drilling equipment since it has been considered that bit life would be substantially reduced. However, in accordance with the present invention an improved downhole reciprocating piston hammer type drill or percussion tool has been developed which is particularly adapted for use with an improved claw type bit, including a bit with replaceable hard metal inserts that may be easily replaced to extend bit life and to minimize the need to disassemble the tool to replace or repair the bit.